The present invention relates generally to testing arrangements, and more particularly to an arrangement for testing phased array antennas which operate in both CW and pulsed modes over multioctave RF frequency range and require very accurate polarization set-on capabilities.
The government has rights in this invention pursuant to Contract No. F 33657-79-C-0083 awarded by the Department of the Air Force.
There are already known electronic systems which employ phased array antennas as their principal radiators into free space. Such phased array antennas include a plurality of antenna elements which are energized while operating in a transmitting mode with different waveforms, with the result that an electromagnetic radiation field develops in the so-called far field, that is, at a certain distance from the phased array antenna, which radiation field is confined to a predetermined spatial sector and scans such sector. Such phased array antenna is usually also used as a receiving antenna from the free space, especially from the aforementioned spatial sector, and the electromagnetic radiation received thereby is often utilized, after having been converted into electric signals representative thereof, for adapting the operation of the circuitry which controls the supply of the above-mentioned different waveforms to the phased array antenna. This is particularly useful in the electronic countermeasures field, where it is important that electromagnetic radiation emitted by the phased antenna array be correlated to electromagnetic radiation received from enemy sources, particularly the polarization of such electromagnetic radiation to be able to convey to the enemy false information about the location of the potential target equipped with the phased array antenna arrangement.
To assure that the phased array antenna arrangement performs in the desired manner, it is necessary to test the electromagnetic radiation pattern of the phased array antenna and the reaction of the phased array antenna arrangement to different types of received electromagnetic radiation at least after the arrangement has been manufactured and/or installed in the respective craft, but more often than not also from time to time or as required after the arrangement has been installed, to make sure that the arrangement still operates in the desired manner. The approach to such testing which is currently used the most is to employ a test enclosure, also called a test hat, which includes equipment capable of measuring or testing the performance of the phased antenna array in the far field, that is, at a region at which the electromagnetic radiation pattern emitted by the phased array antenna is already fully developed. This brings about the advantage that the radiation pattern at this far-field region is relatively simple, so that it is quite easy to process the electrical signals representative of this radiation pattern in the far-field region and detect the performance of the phased array antenna therefrom. However, because of the relatively large distance of the far-field from the phased array antenna, the test enclosure of this type has to have substantial dimensions, which renders its handling rather difficult, especially when used in support facilities that are not specially equipped for performing this task. On the other hand, it was heretofore believed by people active in the area of testing array antennas that it is necessary to perform the testing in the far field, especially since generic near-field solutions require measuring of both amplitude and phase and extensive computational processing, so that such testing arrangements would be costly and subject to serious errors due to tolerances and environment.